1. Technical Field of the Invention
This invention relates to a solar battery comprising a transparent electrode which can be a transparent conductive film of oxide, and a semiconductor layer of non-crystalline silicon or the like, and a metal electrode formed on the transparent electrode in the stated order.
2. Prior Art and its Problems
A tin oxide (SnO.sub.2) film or an indium tin oxide (ITO) film have been extensively employed in the prior art as the materials for the transparent electrode of non-crystalline solar batteries. The fundamental desired characteristics of the transparent electrode are high transmittance, low resistance, and high stability. FIG. 2 shows the structure of a non-crystalline solar battery with a transparent electrode according to the prior art. As shown in FIG. 2, a transparent electrode 2 is formed on a transparent insulated substrate 1, and a photoelectromotive force generating section, namely, a non-crystalline semiconductor layer 3, and a metal electrode 4 are formed on the transparent electrode 2 in the stated order. In addition to the fundamental desired characteristics of a transparent electrode 2 as described above, it would be beneficial to reduce surface reflection loss due to the surface roughness of the transparent electrode. Additional desired characteristics include confinement of light in the semi-conductor layer in order to improve the photoelectric conversion efficiency of the solar battery.
The aforementioned optical confinement effect will be better understood with reference to FIG. 3. The light rays which pass through a transparent insulated substrate 1 are scattered by an uneven surface of transparent electrode 2, and therefore the length of the optical path in a non-crystalline semiconductor layer 3 is increased, as a result of which the amount of light absorption in the photoelectromotive force generating region is increased. If the transparent electrode 2 has an uneven surface as shown in FIG. 3, then the interface between a semiconductor layer 3 and a metal electrode 4 which is formed on the uneven surface is also made uneven. The uneven interface also contributes to the optical confinement effect. A transparent conductive film having the unevenness of its surface thus controlled is essential for forming a high-performance solar battery.
Heretofore, oxide films having an uneven surface as described above were formed according to a method in which the film forming conditions are controlled to make the oxide large in grain size. Alternatively, a method was employed in which the surface of the transparent insulated substrate was made uneven in advance so that the surface of the oxide layer formed thereon is made uneven. However, the former method is disadvantageous in that it is difficult to control the degree of unevenness, and the latter method is also disadvantageous in that the manufacturing process is so intricate that the method is not suitable for either the mass production of solar batteries or for the formation of large solar batteries.